The present invention relates to a device capable of increasing the rotation speed of a magneto motor and, more particularly, to a plurality of magnetic sensors provided in a magneto motor to sense rotor magnets and let the exciting current of stator coils generate variable conduction angles.
To manufacture an electromotor of high operational efficiency, an appropriate value of the torsion coefficient KT must be designed and matched with the operational range of the electromotor, as illustrated with the following formulas.
wherein E is the counter electromotive force voltage (volt), T is the output torsion (Nxe2x88x92m), KE is the counter electromotive force coefficient, KT is the torsion coefficient, xcexa9 is the rotation speed of the armature (rad/sec), Ia is the armature current (ampere), B is the magnetic flux density of the gap (gauss), D is the outer diameter of the armature (cm), L is the superimposed thickness (cm), and Z is the total number of turns of conductors.
As can be seen from the above formulas, the counter electromotive force coefficient KE equals the torsion coefficient KT, and the counter electromotive force coefficient KE is inversely proportional to the rotation speed of the armature xcexa9. Therefore, for a fixed counter electromotive force voltage E, if the normal rated rotation speed of the armature is lower, the value of the counter electromotive force coefficient KE will be relatively higher, while if the normal rated rotation speed of the armature is higher, the value of the counter electromotive force coefficient KE will be relatively lower. If a motor is designed to have a higher normal rated rotation speed of the armature, the value of the torsion coefficient KT will be relatively lower so that the torsion T (T=KTxc2x7Ia) can only be increased with a higher armature current Ia if the motor is operated at a lower rotation speed. If a motor is designed to have a higher torsion coefficient KT, the motor will not accomplish a higher normal rated rotation speed because KT=KE and E=KExc2x7xcexa9. The present invention can let a motor have a higher torsion coefficient KT. Moreover, the present invention can switch to magnetic sensors sensing angle in advance to let the armature of the motor generate the effect of weak magnetic control, hence reducing the magnetic flux density of the armature gap. From the above formulas KE=Bxc2x7Dxc2x7Lxc2x7Z/2 and E=KExc2x7xcexa9, because the magnetic flux density B of the armature gap decreases, the counter electromotive force coefficient KE consequentially decreases. Therefore, the rotation speed of the armature, xcexa9, will inevitably increase.
The torsion coefficient KT of a prior art motor is a single value. For a motor usually operating in the range of lower rotation speeds and sometimes operating in the range of higher rotation speeds (e.g., a light electric vehicle), to let the motor operate in the seldom work range of the highest rotation speed when necessary, because KE=KT, E=KExc2x7xcexa9, and T=KTxc2x7Ia, the torsion coefficient KT and the counter electromotive force coefficient KE must decrease to increase the rotation speed xcexa9 to the seldom work range of the highest rotation speed if the counter electromotive force voltage E is fixed. Because the torsion coefficient KT decreases, and the motor usually operates in the range of lower rotation speeds, the armature current Ia must increase to increase the torsion T because T=KTxc2x7Ia. However, a too large Ia is not good to the operational efficiency of the motor. This can be known from the following formula.
P=I2xc2x7R
wherein P is the dissipated power of the coil of an electromotor, I is the armature current, and R is the impedance of the coil. Therefore, if the torsion of a motor is increased by increasing the armature current, the dissipated power of the stator coil will increase squarely, and heat will be generated in the impedance of the coil. The impedance of the coil will correspondingly rise due to the temperature rise of the metallic coil. This vicious circle will let the motor operate in an environment of high temperature, hence resulting in a worse output efficiency.
A stator portion of a conventional motor is formed by winding a single coil. Therefore, the torsion coefficient KT and the counter electromotive force coefficient KE thereof are consequentially constant values. If a motor is designed to have higher values of the KT and KE, the rotation speed xcexa9 of the armature will decrease proportionally. In the present invention, a plurality of magnetic sensors are provided in a magneto motor to sense the variation of rotating poles of rotor magnets, and at least a magnetic sensor is provided at the position letting the switching angle of the exciting current of stator coils be not orthogonal to the rotating poles of the rotor. Signals sensed by the non-orthogonal switching sensors are outputted to a motor driving and control circuit, which let the exciting current of the stator coils of the motor generate the effect of weak magnetic control, hence increasing the rotation speed of the rotor. The above weak magnetic control device capable of increasing the rotation speed of a motor when necessary can let the motor use magnetic sensors which switch angles with normal exciting current to have a larger value of the torsion coefficient KT. When a motor of larger KT value operates at lower rotation speeds, because the armature current Ia can be decreased proportionally (T=KTxc2x7Ia), the dissipated power of the stator coils of the motor will also decrease (P=I2xc2x7R), thereby reducing the working temperature of the motor and increasing the operational efficiency of the motor operating at lower rotation speeds.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: